In the late 19th and early 20th centuries, automotive wheel design was based on that of bicycle tires having thin walls with high pressure and narrow profiles. The advantage of this, important at that time, was high energy efficiency with low energy loss due to tire flex. Disadvantages were a hard ride and frequent punctures. As time went on, engines became more powerful and fuel less expensive. Freedom from flats and ride comfort took top priority, leading to wider, lower pressure, thicker tires. These tires involved greater energy loss mainly due to tire flex at and near the area of contact with the road. Recently however, energy conservation has once again become of prime importance. The need for higher energy efficiency in the wheel, among other automotive subsystems, is paramount.
Under smooth road conditions, the ideal energy conserving tire has thin walls and is inflated to high pressure. The tire is supported by the rim which functions as a rigid support. A narrow high pressure bicycle tire is an example. A small amount of tire flex occurs at or near the road contact, causing minimal energy loss.
Under rough conditions with large road obstructions, shock absorption and cushioning are the major requirements which a low pressure, large chambered tire can satisfy. Conventional automotive tires meet these requirements well. These tires rely on a single inflated low pressure thick-walled air chamber for operation on both smooth and rough roads. Thus a conventional tire is largely biased towards cushioning on rough roads, while sacrificing the energy saving characteristics of narrow high pressure tires.
Past attempts have been made to design energy conserving multichambered tires. U.S. Pat. Nos. 4,293,017 and 5,109,905 (Lambe) disclose a two-chambered tire, with the goal of reducing tire flex and conserving energy. An outer high pressure tread chamber is intended to simulate a high pressure pneumatic tire. An inner low pressure chamber is intended to simulate a conventional low pressure tire with cushioning effect. However, Lambe's tire would provide at most a small improvement in efficiency over a conventional tire, for two reasons. Without internal restraint bands to position the outer chamber relative to the hub, a very high outer chamber pressure would be required to stiffen the tread sufficiently to adequately reduce tire flex both in the low pressure chamber and near the road contact. There is nothing present that enables simulation of the rigid support provided to a narrow high pressure tire by its rim. Also, even if the outer chamber were stiffened substantially, without internal restraint bands the outer chamber would not remain centered on the rotational axis; thus the sidewalls would flex to about the same extent as with a conventional tire. Much of the outer chamber would move vertically in response to a road obstruction, possibly leading to an actual reduction in efficiency. The outer chamber may have increased stiffness because of the high pressure, but the restoring force profile (i.e. the restoring force as a function of overall tire deformation) is similar to that of a conventional automotive tire. As a result, Lambe's tire cannot truly and effectively simulate a high pressure pneumatic tire on a smooth road.
References to multi-chambered tires for the purpose of reducing the effects of punctures occur, for example in U.S. Pat. No. 6,470,935 (Fulsang), U.S. Pat. No. 2,572,594 (Bushemi), and U.S. Pat. No. 580,884 (Murphy). These examples make no reference to energy saving features.
References to hub protectors exist, for example U.S. Pat. No. 7,100,654 (Boiocchi, et al), U.S. Pat. No. 5,885,383 (French), and U.S. Pat. No. 4,922,981 (Pompier). These devices serve to reduce damage to the hub and rim after a puncture, but are not designed to function as shock absorbers or as a component of suspensions.
The present device features a tire which meets the requirements for rough and smooth roads in such a manner that each of the two requirements comes into play only when required by the specific road condition. Thus each of the two requirements can be met separately and optimally. On a smooth road, an internal restraint band holds the outer high pressure chamber in a position concentric with the hub and axis. On a rough road, that part of the tire near the road contact buckles inward toward the hub, bringing the cushioning effect of the low pressure chamber and the hub protector into play. Additional reductions in energy consumption can be gained by incorporating an electric hub motor, which reduces or eliminates the need for the typical drive train implemented between the engine and the conventional wheel.
The previous attempts at producing a tire design combining the advantages of energy conservation on smooth roads and cushioning on rough roads have proven inadequate. The present device however, meets these requirements and more: (1) simulation of a high pressure pneumatic tire on smooth roads, (2) simulation of a cushioning effect of a conventional low pressure tire on rough roads, (3) functioning as a shock absorber and suspension on rough roads, and (4) safety features to mitigate the effect of punctures.